1. Field of the Invention
The present invention relates to fuel delivery systems for motor vehicles.
2. Description of the Related Art
In the continuing effort to reduce evaporative emissions from motor vehicles, "returnless" fuel systems are seen as a promising way to do so. A conventional fuel system has a fuel line connecting a fuel pump with a fuel rail on the engine of the motor vehicle. Connected to the fuel rail are one or more fuel injectors. A second fuel line runs from a bypass fuel pressure regulator on the fuel rail to the fuel tank of the motor vehicle to return unused fuel to the fuel tank. This fuel that returns to the fuel tank has often been heated by the heat of the engine, by exhaust heat and by heat from the underbody of the vehicle. One disadvantageous result from an emissions standpoint is the accumulation of fuel vapor in the fuel tank due to the return of heated fuel.
Returnless fuel systems eliminate the fuel line which returns fuel from the fuel rail to the fuel tank. Instead, the fuel system is designed to supply the proper amount of fuel to the fuel rail, so there is no excess.
One proposed returnless fuel system is disclosed in U.S. Pat. No. 5,044,344, issued to Tuckey et al. In this system, the speed of a fuel pump motor is controlled in accordance with feedback from a fuel pressure sensor. Although such a system may generally be effective, alternative systems may be more economical than an electronic system. Further, other systems may be able to respond more quickly to transient conditions than a system which operates based on controlling the speed of a fuel pump.